1. Field of the Invention
The present invention relates to a method for hardening a one-package composition comprising an epoxy resin and a hardener.
In particular, the present invention is useful in the fields of civil engineering and construction, corrosion protection and precision electronic parts, where it is desired to obtain an intended curing characteristic by heat treatment at a relatively low temperature of about 60.degree. to 70.degree. C. for a period of one or two hours or less or for a relatively short period of several minutes at a higher temperature of more than 80.degree. C.
The reasons therefor are that in fields involving a lot of outdoor work such as civil engineering and construction and corrosion protection, etc., it is difficult to find a heat source which permits heat treatment at a high temperature for a long period of time, and in the field of precision electronic parts it is difficult to maintain reliability due to problems of heat resistance, etc., of adherends.
2. Description of Related Art
In the fields of civil engineering and construction, corrosion protection and precision electronic parts, it has been a general practice to use a cold-curing two-package epoxy resin composition for rapid curing at a relatively low temperature.
However, such a two-package epoxy resin composition has the following defects: complicated steps of weighing, mixing, stirring, etc., just before use are required; lack of reliability due to possible errors in weighing; unstable product quality due to very short pot life; difficulty in obtaining its characteristics as designed; large loss of raw material; etc. Due to these defects, a two-package epoxy resin composition has been very disadvantageous where a long working period is required, and adhesives and coating compositions are frequently used, such as, e.g. in the fields of civil engineering and construction, corrosion protection, etc.
Many one-package epoxy resin compositions have been under recent development, and some of them are commercially available. In order to cure one-package epoxy resin compositions, it has been a usual method to heat them at a temperature of not less than 80.degree. C. for several hours.
However, in fields where operations are mainly carried out outdoors, such as in the fields of civil engineering and construction, corrosion protection, etc., heating at a temperature of not less than 80.degree. C. for several hours is very difficult. Further, in the assembling of precision electronic parts where there is a risk of parts being damaged when they are exposed to a high temperature for a long period of time, it has been practically impossible to cure adhesives by heating the parts at a temperature of not less than 80.degree. C. for a long period of time.